The present invention relates to a detector system for direct internal dosimetry in a person, which system is capable of measuring the actual dose equivalent to which the person is exposed.
Basically such systems are known, for example, from IEEE Transactions on Nuclear Science, Vol. N5-J4, No. 1, 187, pages 606-610.
For radioactive substance ingestion monitoring for work-related radiation exposure of persons it is the object to determine the radioactivity exposure of the persons so that the limits set by the government are not exceeded. In addition it is necessary for the monitoring procedure to make sure that the supplemental doses resulting from active particle ingestion will not exceed the limits for body or organs as determined by law.
Body contamination monitoring can be performed by measuring the activity before entry into the body (monitoring of ambient air, that is, breathing air), by measuring the activity after entry into the body (direct monitoring) or by measuring the activity after exiting the body (excrement monitoring). Generally, direct monitoring supplies the most reliable evidence with regard to radioactivity ingestion and the resulting equivalent dosis. Direct monitoring however is usable only in connection with radionuclides which emit gamma or x-ray radiation of sufficient energy and intensity. However, this prerequisite is present in many areas of nuclear technology and of medicine so that, in these areas, direct monitoring is generally preferred.
The direct monitoring of body activity is performed with full or partial body counters which, with monitoring periods of between 5 and 20 minutes, measure the activity in the whole body or, respectively, in certain predetermined parts of the body. The persons to be monitored are checked after predetermined periods wherein the check-up frequency is dependent on the limits for the activity ingestion, the biological half-life and the lower detection limit of the whole or partial body monitors. Generally, the check-up frequencies are between 1 and 12 check-ups per year.
If, during such a routine check-up, a significant body activity is discovered, it will first be necessary to estimate the cause of the activity ingestion and, in a second step, to estimate the resultant equivalent dosis. For this, the following pieces of information are needed:
ingestion time, that is, a time sample of the activity ingestion; PA1 path of ingestion and chemical composition of the ingested activity; PA1 individual metabolism; PA1 contribution of earlier ingestions to the actual measured value. PA1 It is practically impossible to provide general qualification features such as recognition limits, detection limits and reliability ranges for the activity ingestion and the resulting equivalent dosis. Consequently, it is very difficult to compare different monitoring procedures with one another. Furthermore, it is very difficult to define minimum requirements for the ingestion measurement locations. PA1 It is very difficult to document the measurement values in such a manner that they can be repeated in a later test measurement. These difficulties are especially grave in the documentation of the measurement results in the radiation exposure cards of persons with changing workplace. The difficulties are present to an even greater degree if the results of the internal radiation exposure are to be documented in a central dosis recording location. PA1 If a person with a given ingestion is tested at different institutions it has been found that often quite different activity ingestion, that is, different equivalent dosis, have been estimated. This can be highly confusing especially with a change of workplace. PA1 H.sup.1 (T,S) is the equivalency dosis effect in nSv/d generated in a particular target organ by nuclide deposition in a particular source organ S; PA1 A.sub.S is the activity of the nuclide deposition in the source organ S in Bq; PA1 SEE(T,S) is the so-called specific effective energy of S on the basis of T (the energy per mass unit absorbed by the decay of the nuclide deposited in S, multiplied by a quality factor corresponding to the radiation quality of the respective nuclide in MeV/g/decay. PA1 Zi(S) is the counting rate of the i.sup.th detector for nuclide depositions in the source organ S in imp/s; PA1 e.sub.i (S) is the sensitivity of the i.sup.th detector for nuclide depositions in the source organ in imp/s/Bq; PA1 A.sub.S is the activity in the source organ S in Bq. PA1 M(S) is the measurement value of the system for nuclide deposition in the source organ S in imp/s; PA1 .alpha..sub.i is the weighting factor for the i.sup.th detector with the normalization .SIGMA..sub.i .times..alpha..sub.i =1; PA1 A.sub.S is the activity in the source organ S in Bq; PA1 m(S) is the system sensitivity for nuclide depositions in the source organ S in imp/s/Bq EQU m(S)=.SIGMA..sub.i [.alpha..sub.i .times.e.sub.i (S)]
These pieces of information are generally not available or they are available only to an insufficient degree so that the estimate may be quite inaccurate. With nuclides with a relatively long biological half-life and with relatively simple and well-known metabolism behavior such as cesium-137, errors of between 25% and 100% are possible. With other nuclides the error may well be greater than a factor of 2.
Because of the multitude of the ingestion possibilities it is extremely difficult to define generally valid procedures for estimating the activity ingestion and the resulting equivalent dosis. The procedures given in the guidelines for the implementation of the radiation protection rules are necessarily a compromise between the clarity of the representation and the multiplicity of the required detail information. For this reason, numerous vague information details are entered in praxis during implementation of the guidelines. These vague factors result, among others, in the following difficulties:
It is the object of the present invention to provide a detector system for internal dosimetry with which the effective equivalency dosis of a person can be directly measured.